Plasma display panel comprising a terbium(III)-activated fluorescent substance

ABSTRACT

The invention relates to plasma display panels with a segmented fluorescent layer ( 9 ), in which green color filter layers ( 14 ) of Pr3+-containing materials of green-emitting color segments are deposited between the fluorescent layer ( 9 ) and the carrier plate ( 2 ), which improve the color dot of the green light which is emitted by the Tb3+-activated fluorescent substance.

The invention relates to a plasma display panel equipped with a frontplate which has a glass plate on which a dielectric layer and aprotective layer are deposited, with a carrier plate covered by asegmented fluorescent layer which contains red-emitting color segmentsof a red-emitting fluorescent substance, blue-emitting color segments ofa blue-emitting fluorescent substance and green-emitting color segmentsof a green-emitting Tb³⁺-activated fluorescent substance, has a ribstructure which divides the space between front plate and carrier plateinto plasma cells which are gas-filled, with one or more electrodearrays on the front plate and the carrier plate for generating silentelectrical discharges in the plasma cells.

Plasma display panels make high-resolution color pictures possible,large display panel diagonals and are of compact structure. A plasmadisplay panel has a hermetically sealed glass cell which is gas-filled,with grid-like arranged electrodes. By applying an electric voltage, agas discharge is caused which generates light in the ultraviolet range(145 to 185 nm). This light can be transformed to visible light byfluorescent substances and be emitted to the viewer through the frontplate of the glass cell.

For plasma display panels are used fluorescent substances which arehighly efficient under vacuum-UV excitation. Frequently usedgreen-emitting fluorescent substances are, for example, Zn₂SiO₄:Mn (ZSM)or BaAl₁₂O₁₉:Mn (BAL). The two materials show a saturated green emissioncolor with a high y value of y>0.7. A disadvantage of the two materialsis a relatively long decay time t_(1/10), which is about 30 ms forZn₂SiO₄ with 2.5% Mn. This is caused by the fact that the spin of thetransition ⁴T₁→⁶A₁, which is relevant for the emission of the light, isforbidden. In addition, the decay time t_(1/10) and the color point ofan Mn²⁺-activated fluorescent substance strongly depend on theconcentration of Mn²⁺. A further disadvantage is the sensitivity of Mn²⁺as against an oxidation to Mn³⁺ or Mn⁴⁺, which reduces the stability ofthe fluorescent substance.

Contrary to this, Tb³⁺-activated fluorescent substances are stable asregards temperature and picture, because Tb³⁺ is hard to be oxidized toTb⁴⁺. A further advantage of this fluorescent substance as againstMn²⁺-activated fluorescent substances is their shorter decay timet_(1/10), which amounts to 2 to 10 ms depending on the host lattice.

Therefore, U.S. Pat. No. 6,004,481 describes a green-emittingTb³⁺-activated fluorescent substance for applications in plasma displaypanels, which has the composition (Y_(1-x-y-z)Gd_(x)Tb_(y)Ce_(z))BO₃,where 0.0<x<0.2, 0.01<y<0.1 and 0.0<z<0.1.

A large disadvantage of Tb³⁺-activated fluorescent substance is itsyellow-green color point, which has a low y value of y<0.62.

It is an object of the invention to provide a plasma display panel witha Tb³⁺-activated fluorescent substance whose green sub-pixels producelight with an improved color dot.

The object is achieved by a plasma display panel equipped with a frontplate which has a glass plate on which a dielectric layer and aprotective layer are deposited, with a carrier plate covered by asegmented fluorescent layer which contains red-emitting color segmentsof a red-emitting fluorescent substance, blue-emitting color segments ofa blue-emitting fluorescent substance and green-emitting color segmentsof a green-emitting Tb³⁺-activated fluorescent substance, has a ribstructure which divides the space between front plate and carrier plateinto plasma cells which are gas-filled, with one or more electrodearrays on the front plate and the carrier plate for generating silentelectrical discharges in the plasma cells, and has a green color filterlayer between a green-emitting color segment of the fluorescent layerand the carrier plate.

Besides a strong light emission with a wavelength between 540 and 550nm, Tb³⁺-activated fluorescent substances also have, although clearlyweaker, emission bands in the yellow and red spectral area. Theintensity of these emission bands can be reduced by a green color filterlayer and thus the y values of the color points of the Tb³⁺-activatedfluorescent substance can be increased.

The advantageously selected materials for a green color filter layer asclaimed in claim 2 and claim 3 have a high transmission between 530 and550 nm.

The advantageously selected Tb³⁺-activated fluorescent substances asclaimed in claim 4 are highly efficient green-emitting fluorescentsubstances when excited with VUV light.

These and other aspects of the invention are apparent from and will beelucidated with reference to the embodiments described hereinafter.

In the drawings:

FIG. 1 shows the structure and the function principle of a single plasmacell in an AC plasma display panel with a green-emitting color segmentof the fluorescent layer and a green color filter layer.

As shown in FIG. 1 a plasma cell of an AC plasma display panel with aco-planar arrangement of electrodes has a front plate 1 and a carrierplate 2. The front plate 1 has a transparent plate 3, for example madeof glass on which are deposited a dielectric layer 4 which preferablycontains low-melting glass and on top of it a protective layer 5 whichpreferably contains MgO. Parallel striped discharge electrodes 6, 7which are covered by the dielectric layer 4 are deposited on thetransparent plate 3. The discharge electrodes 6, 7 are made for exampleof metal, ITO or a combination of a metal and ITO. The dischargeelectrodes 6, 7 preferably each comprise a strip of ITO on which anarrower layer of Al or Ag is deposited as a bus electrode. The carrierplate 2 is preferably made of glass and on the carrier plate 2 aredeposited parallel strip-like address electrodes 10 of, for example, Agwhich run perpendicularly to the discharge electrodes 6, 7. Theseaddress electrodes 10 are covered by a fluorescent layer 9 which emitslight 13 into one of the three basic colors red, green or blue. For thispurpose the fluorescent layer 9 is subdivided into a plurality of colorsegments. A rib structure 12 with separating ribs of preferablydielectric material forms individually drivable plasma cells in whichsilent electric discharges occur.

There is a gas in the plasma cell and also between the dischargeelectrodes 6, 7 of which one alternately works as a cathode or an anoderespectively. The gas may be, for example, a rare gas, a mixture of raregases with Xe as an UV light-emitting component, nitrogen or a mixtureof nitrogen and at least one rare gas such as, for example, He, Ne, Kror Xe. After igniting the surface discharge as a result of which chargescan flow along a discharge path between the discharge electrodes 6, 7 inthe plasma area 8, a plasma is formed in the plasma area 8 by whichplasma radiation 11 is generated in the UV range mostly in the VUV rangedepending on the composition of the gas. The radiation 11 excites thefluorescent layer 9 to radiate, which layer emits visible light 13 whichcomes out through the front plate 1 and thus represents a lighting doton the display panel. The fluorescent layer 9 is subdivided into aplurality of color segments. Customarily the red, green or blue-emittingcolor segments of the fluorescent layer 9 are deposited in the form ofperpendicular triple lines. A plasma cell with a color segment forms aso-called sub-pixel. Three adjacent plasma cells having each a red,green or blue-emitting color segment together form a pixel, or alsocalled picture element.

Between the back of the fluorescent layer 9 of a green-emitting colorsegment and the carrier plate 2 there is a green color filter layer 14.In the embodiment shown in FIG. 1 the green color filter layer 14extends to the side walls of the plasma cells between the fluorescentlayer 9 of a green-emitting fluorescent substance and the rib structure12. However, it is not necessary for the green color filter layer 14 tocover the whole back wall or all the side walls of the plasma cells. Itis sufficient if the back wall and/or the side walls are covered atleast partly.

Suitable materials for a green color filter layer 14 have a hightransmission between 530 and 550 nm and absorb at 490, 590 and 620 nm.Eminently suitable are Pr³⁺-containing materials such as PrPO₄,[Pr(PO₃)₃]_(n), PrF₃, PrOCl, PrOF, PrOBr, Pr₃Al₅O₁₂, PrBO₃, Pr₂SiO₅,Pr₂Si₂O₇ or PrB₃O₆, because Pr³⁺ strongly absorbs at 490 nm and 590 nm.Particularly PrPO₄ and [Pr(PO₃)₃]_(n) are suitable for use in a greencolor filter layer 14.

The green color filter layer 14 can simultaneously work as a reflectorfor green light that was not emitted in the direction of the front plate1.

As manufacturing methods for such a green color filter layer 14 may beused both dry coating methods, for example, electrostatic separation orelectrostatic supported dry spraying and wet coating methods, forexample, screen printing, dispersion methods in which a suspension isintroduced with a nozzle moving along the channels, or sedimentationfrom the liquid phase. The same methods are suitable for manufacturingthe fluorescent layer 9.

A Tb³⁺-activated fluorescent substance such as, for example,(Y_(x)Gd_(1-x-y)) BO₃:Tb_(y)(0≦x≦1, 0≦y≦1), LaPO₄:Tb,(Y_(x)Gd_(1-x-y))₃Al₅O₁₂:Tb_(y)(0≦x≦1, 0≦y≦1), CeMgAl₁₁O₁₉:Tb,GdMgB₅O₁₀:Ce,Tb, (Y_(x)Gd_(1-x-y))₂SiO₅:Tb_(y)(0≦x≦1, 0≦y≦1),(In_(x)Gd_(1-x-y))BO₃:Tb_(y)(0≦x≦1, 0≦y≦1),(Y_(1-x-y)Gd_(x))₂O₂S:Tb_(y)(0≦x≦1, 0≦y≦1), LaOBr:Tb, LaOCl:Tb orLaPO₄:Ce,Tb is used as a green-emitting fluorescent substance in thefluorescent layer 9. The concentration of Tb³⁺ in the fluorescentsubstances is situated preferably between 2 and 20 mol %. Preferably(Y_(0.7)Gd_(0.2))BO₃:Tb_(0.1) is used as a Tb³⁺-activated fluorescentsubstance.

For example (Y_(x)Gd_(1-x))BO₃:Eu (0≦x≦1), Y(V_(x)P_(1-x))O₄:Eu (0≦x≦1)or Y₂O₃:Eu may be used as a red-emitting fluorescent substance.Preferably BaMgAl₁₀O₁₇:Eu is used as a blue-emitting fluorescentsubstance.

It may be advantageous for a red color filter layer to be locatedbetween the color segments of the fluorescent layer 9 of a red-emittingfluorescent substance and the carrier plate 2 and/or a blue color filterlayer between the color segments of the fluorescent layer 9 of ablue-emitting fluorescent substance. For example, Fe₂O₃, TaON orCdS—CdSe may be used as pigments for a red color filter layer and, forexample, CO₀—Al₂O₃ as pigments for a blue color filter layer orultramarine. The manufacturing of these color filter layers takes placein accordance with a method described for the manufacture of the greencolor filter layer 14.

Basically, a green color filter layer 14 may be used in all types ofplasma display panels such as, for example, in AC plasma display panelswith or without a matrix arrangement of the electrode arrays or DCplasma display panels.

EXAMPLE OF EMBODIMENT 1

On a carrier plate 2 with a rib structure 12, a green color filter layer14 of PrPO₄ was deposited in the plasma cells in which later on therewould be a green-emitting color segment of the fluorescent layer 9.Subsequently, (Y_(0.7)Gd_(0.2))BO₃:Tb_(0.1) was deposited as agreen-emitting fluorescent substance on the green color filter layer 14by means of screen printing. Then the red and blue-emitting colorsegments were established with Y₂O₃:Eu or BaMgAl₀O₁₇:Eu, respectively,as fluorescent substances. The carrier plate 2 was used together with afront plate 1 and a gas mixture with xenon as a component generating UVlight to build a plasma display panel with an improved color dot for thegreen pixels.

The color point (x,y) of the green sub-pixel in such a plasma displaypanel was x=0.323, y=0.626. By comparison, the color point (x,y) of thegreen sub-pixels of a comparable plasma display panel without a PrPO₄xgreen color filter layer was 14 x=0.331, y=0.584.

EXAMPLE OF EMBODIMENT 2

A plasma display panel similar to the example of embodiment 1 describedwas made with only y₂SiO₅:5% Tb being used as a green-emittingfluorescent substance.

The color dot (x,y) of the green sub-pixels in such a plasma displaypanel was x=0.315, y=0.638. By comparison the color dot (x,y) of thegreen sub-pixels of a comparable plasma display panel without a PrPO₄green color filter layer 14 was x=0.335, y=0.615.

1. A plasma display panel equipped with a front plate (1) which has aglass plate (3) on which a dielectric layer (4) and a protective layer(5) are deposited, with a carrier plate (2) covered by a segmentedfluorescent layer (9) which contains red-emitting color segments of ared-emitting fluorescent substance, blue-emitting color segments of ablue-emitting fluorescent substance and green-emitting color segments ofa green-emitting Tb³⁺-activated fluorescent substance, has a ribstructure (12) which divides the space between front plate (1) andcarrier plate (2) into plasma cells which are gas-filled, with one ormore electrode arrays (6, 7, 10) on the front plate (1) and the carrierplate (2) for generating silent electrical discharges in the plasmacells and has a green color filter layer (14) between the fluorescentlayer (9) of a green-emitting color segment and the carrier plate (2).2. A plasma display panel as claimed in claim 1, characterized in thatthe green color filter layer (14) contains Pr³⁺-containing materials. 3.A plasma display panel as claimed in claim 2, characterized in thatPr³⁺-containing materials are selected from the group PrPO₄,[Pr(PO₃)₃]_(n), PrF₃, PrOCl, PrOF, PrOBr, Pr₃Al₅O₁₂, PrBO₃, Pr₂SiO₅,Pr₂Si₂O₇ and PrB₃O₆.
 4. A plasma display panel as claimed in claim 1,characterized in that the green Tb³⁺-activated fluorescent substance isselected from the group (Y_(x)Gd_(1-x-y))BO₃:Tb_(y)(0≦x≦1, 0≦y≦1),LaPO₄:Tb, (Y_(x)Gd_(1-x-y))₃Al₅O₁₂: Tb_(y)(0≦x≦1,0≦y≦1), CeMgAl₁₁O₁₉:Tb,GdMgB₅O₁₀:Ce,Tb, (Y_(x)Gd_(1-x-y))₂SiO₅:Tb_(y)(0≦x≦1,0≦y≦1),(In_(x)Gd_(1-x-y)) BO₃:Tb_(y)(0≦x≦1, 0≦y≦1),(Y_(1-x-y)Gd_(x))₂O₂S:Tb_(y)(0≦x≦1, 0≦y≦1), LaOBr:Tb, LaOCl:Tb andLaPO₄:Ce,Tb.